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Integrated Pest Management Program

Department of Plant Science and Landscape Architecture, Department of Extension

Fact Sheets > Greenhouse > Biological Controls

Biological Control of Fungus Gnats

Fungus gnats (Bradysia spp.) are a common greenhouse pest, especially in the moist environment common in propagation greenhouses. Fungus gnat larvae feed upon young cuttings and plugs, causing root injury and death. Fungus gnats also help spread pathogens including Fusarium and Thielaviopsis. 

Figure 1: Fungus gnat larvae root feeding injury on Catharanthus (Annual Vinca). Photo by L. Pundt

Biology and Life Cycle

The fungus gnat's life cycle from egg to adult may be completed in as little as three to four weeks depending on the temperature. Eggs are laid in cracks and crevices in the media surface and mature in four to six days. Fungus gnat larvae feed and develop for about two weeks at 72oF. 

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Figure 2: Close-up of fungus gnat larvae.  Photo by L. Pundt

 Pupation occurs in the soil. After four to five days, adults emerge. Overlapping and continuous generations make control difficult.  Fungus gnats are a common problem on annual vinca, geraniums, begonias, poinsettias, sedum, and bulb crops, especially with growing medium with a high percentage of peat moss or composted bark.  Peanut hulls used in growing media also provide an ideal hiding place. 

Scouting

 A regular monitoring program is needed for early detection and to insure the success of a biological control program. Use yellow sticky cards placed horizontally at the media surface to attract adults.

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Figure 3: Horizontal placement of sticky cards. Photo by L. Pundt

Figure 4: Adult fungus gnat on sticky card. Photo by L. Pundt

Check yellow sticky cards weekly. For more see:  Identifying Some Pest and Beneficial Insects on Your Sticky Cards on the IPM website.   

Potato chunks or plugs can be placed on the media surface to attract larvae. Inspect the potato slices after 2 days.  Inspect root systems for overall health and for signs of damage from fungus gnat feeding (blunt root tips).

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Figure 5: Fungus gnat feeding damage to poinsettia plug. Photo by L. Pundt

 

Figure 6:  Fungus gnat feeding damage. Photo by L. Pundt

Cultural controls (avoiding overwatering, avoiding puddling on the floors, rigorous weed controls, and controlling algae) are critical before starting a biological control program for fungus gnats.

Soil dwelling predatory mite (Hypoaspis miles (= Stratiolaelaps scimutus), the rove beetle, Atheta coriaria (= Dalotia coriaria) and entomopathogenic nematodes (Steinernema feltiae) can all be used in your biological control program. The growing medium should be moist before applying these natural enemies. 

Although not commercially available, predatory hunter flies (Coenosia attenuata), and the parasitoid Synacra pauperi may also help to manage fungus gnats.

Predatory Mites

A native, soil-dwelling generalist predatory mite, Hypoaspis miles (= Stratiolaelaps scimitus) feeds on fungus gnat larvae as well as  other soil dwelling insects such as thrips pupae, springtails  and shore fly larvae.  However, Hypoasis prefers to feed upon the first instar fungus gnat larvae.   If small prey insects are scarce, these predatory mites can survive by scavenging on plant debris and algae.  Hypoasis inhabits the top ½ inch of soil and does not survive in standing water. Adults are tan in color and less than 1 mm long.  Hypoaspis aculifer also feeds upon bulb mites as well as fungus gnat larvae.

Hypoaspis is shipped in an inert carrier with all stages of the predatory mites with bran or mold mites that are a food source for the predatory mites.   This carrier can be distributed over the media surface, especially when pots are placed close together. However, these predatory mites won’t move through an entire greenhouse from a single introduction point.  Apply to moist not saturated growing media.  Applications can also be directed to the soil under greenhouse benches.  Avoid mixing H. miles into the growing media prior to planting as this decreases survival.  

Hypoaspis life cycle from egg to adult is about 18 days at 68°F. They do not go into diapause in the winter. Hypoaspis predatory mites are best used before fungus gnat populations become established or while numbers are still low. If fungus gnat populations are established, use with Bacillus thuriengienis subsp. israelensis or entomopathogenic nematodes.

Tips for H. miles use

  • Use preventatively, at planting time.
  • Do not refrigerate. They don’t store well. 
  • Do not mix into the growing media because they will not survive. 
  • Minimum media temperature is 60°F, they become inactive below 59°F
  • Media should be moist, not wet.
  • If you have dirt floors, it may be helpful to treat those areas also.  Treating the perimeter of the greenhouse may also help.
  • To evaluate quality, place a small sample of the mites on a sheet of white paper. Hypoaspis will be tan and will move quickly. The bran mites are translucent, white and move slowly. 
  • Apply to the media surface, not too near the plant stem.
  • Consult with your supplier for compatibility information with other pesticides or with the following resources on the Internet:

- Pesticide Side Effects Database – www.koppert.com

- Pesticide Side Effects Database - www.biobest.be

Rove Beetles

Rove beetles (Atheta = Dalotia) coriaria are generalist predators that feed upon the larvae of fungus gnats, and shore flies in the growing media. They prefer fungus gnat larvae compared to shore fly larvae or thrips pupae.

Adults are slender, dark brown to black hairy beetles, about 1/8 of an inch long, with very short wing covers. Because adults can fly, this helps them disperse in the greenhouse from the release site.  Larvae are cream colored to brown, depending upon their age. Both stages are primarily found in the growing media, especially in cracks and crevices. Once established in a greenhouse, they will be there year round, but population levels vary depending upon fungus gnat populations.

Figure 7: Rove Beetle Adult, Photo by L. Pundt

Rove beetles life cycle from egg to adult is about three weeks at 77° F. Adult beetles are active for about 3 weeks. Adult females lay about 8 eggs per day for the first two weeks after they mature. Eggs hatch in 3 to 4 days into creamy white larvae. (There are three larval stages after which they pupate.)    Because rove beetles are generalist predators, they may feed upon H. miles.   Temperatures between 65 - 80 ˚F and a relative humidity of 50 to 85% are optimum for their survival.   Rove beetles are commercially available as adults mixed in inert material.

Figure 8:  Application of Rove Beetles in piles. Photo by L. Pundt

 

Tips for Atheta (Dalotia) coriaria use

  • Adults are nocturnal so are best released in the evening.
  • Make piles on soil or pots.  (photo)
  • They tend to hid in cracks and crevices in the growing media, so may be difficult to find when scouting.
  • Rove Beetles are compatible with beneficial nematodes.
  • Check with your supplier for pesticide compatibility information or with the following resources on the Internet:

- Pesticide Side Effects Database – www.koppert.com

- Pesticide Side Effects Database - www.biobest.be

Entomopathogenic Nematodes

 Nematodes are small, colorless, unsegmented, cylindrical round worms that occur naturally in soils throughout the world. Entomopathogenic means to cause diseases (pathogenic) to insects (entomon from the Greek word for insect).  Insect parasitic nematodes are primarily found in the families Steinernema and Heterorhabditis. Different species may work best against different pests. S. feltiae is primarily used against fungus gnat larvae, and thrips pupae in the soil.

The nematode’s life cycle consists of eggs, four larval stages and the adults.   The third instar juvenile stage is the infective stage. This stage searches out susceptible insect hosts by detecting excretory products, carbon dioxide and temperature changes. S. feltiae enter the insect host through body openings. They multiply within the host and release a symbiotic bacterium (Xenorhabdus) whose toxin kills the fungus gnat larvae.  The larvae are killed in one to two days by septicemia (blood poisoning) and are difficult to find.  More than one generation of nematodes may develop in dead host insect. The infective juveniles exit the dead body and search for new hosts to infect.  The nematodes will stay active in the media for about 10 to 14 days. They are best applied to moist media, in the evening or during cloudy days and care should be taken not to flush them out of the growing media.

S. feltiae (NemaShield, Nemasys or Entonem) are applied as a soil drench treatment against fungus gnat larvae. Preventative applications to moist soils work best. 

See Beneficial Nematodes: An Easy way to Begin Using Biological Control in the Greenhouse for specific tips on their use.

However, unlike many traditional pesticides there is no REI (an added bonus in propagation houses), nor possibility that the fungus gnat larvae will develop resistance. No adverse effects have been shown against non-target organisms in many different field studies and they are completely safe to humans. Like any biological control agent, they are best used preventively, before an outbreak occurs.

 

Natural Enemies Not Commercially Available  

Hunter Flies

Growers may notice hunter flies (Coenosia attenuata) on their yellow sticky cards.  Hunter flies may be introduced on new plant material.   The hunter fly is in the same family as a housefly but is smaller (1/8 to ¼ inches).  Males have place yellow legs and females have black legs.  Males are a lighter grey than the females.   Hunter flies may be confused with shore flies, but hunter flies have wings that are clear and may appear iridescent as the hunter fly adults perch on plant leaves in the full sun.  These aerial predators will catch fungus gnats or shore flies on the wing.

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Figure 9: Close-up of hunter flies perching on a leaf. Photo by L. Pundt

 

Figure 10: Adult hunter flies on sticky card. Photo by L. Pundt

Hunter flies are also about twice as large as shore flies.  Hunter fly larvae will also feed upon fungus gnat larvae.  Most of their life cycle is in the soil. 

 

Parasitic Wasps

Parasitic wasps (Synacra flies) are a natural enemy of fungus gnats and may be seen on yellow sticky cards, especially in unsprayed greenhouses.

Entomopathogenic nematodes, soil dwelling predatory mites, rove beetles are all part of a biological control program for fungus gnats.   For growers just starting biological controls, beginning with biological control of fungus gnats is often one of the easiest ways to begin. 

 

By Leanne Pundt, Extension Educator, University of Connecticut, 2007, Revised 2014.

 

References:

Cloyd, C. 2003. Do Beneficial Nematodes Really Work? GrowerTalks. November 2003. 72-74.

Cloyd, R. 2004. Rove beetle may be an option for fungus gnat control. GMPro. Nov 2004. 74-75.

Harris, M.A., Oetting, R.D. and W.A. Gardner. 1995. Use of entomopathogenic nematodes and a new monitoring technique for control of fungus gnats, Bradysia coprophila (Diptera: Sciaridae) in floriculture. Biological control 5: 412-418

Hoebeke, E. R., E. Sensenbach. J. Sanderson, and S. Wraight. 2003. First Report of Coenosia attenuata Stein (Diptera: Muscidae), an Old World ‘Hunter Fly’ in North America. Proc. Entomol. Soc. Wash. 105(3):769-775.

Gaugler, R. Nematodes (Rhabditida: Steinernematidae & Heterhabditidae). Biological Control: A Guide to Natural Enemies of North America. http://www.biocontrol.entomology.cornell.edu/pathogens/nematodes.php

(Accessed 9/14)

Georgis, R., H. Kaya and R. Gaugler. 1991. Effect of steinernematid and heterorhabditid nematodes on nontarget arthropods. Environ. Entomol. 20:815-22. 

Lamb, E. and B. Eshenaur. 2014. Greenhouse Biocontrol Workbook.  NYS Integrated Pest Management Program. Cornell University Cooperative Extension.  84 pp. http://www.nysipm.cornell.edu/  Available online at:  http://www.nysipm.cornell.edu/nursery_ghouse/biocontrol_wkbk_10-31-13.pdf

Malais, M.H. and W. J. Ravensberg. 2003. Knowing and Recognizing: The biology of glasshouse pests and their natural enemies. Koppert Biological Systems and Reed Business Information. The Netherlands.  288 pp.

Murphy. G. 2004. The Rove Beetle Atheta coriaria in Commercial Greenhouses. Ontario Ministry of Agriculture and Food. 4 pp.

Sensenbach, E., J. Sanderson and S. Wraight. 2004. Hunter Flies: Good Guys in the Greenhouse. GrowerTalks. August 2004. 85-86.

Smith, T. and L. Pundt. 2014. Greenhouse Pest Guide web App.  http://tiny.cc/greenhousepestguide.

Stack, Lois Berg. (Ed). 2014-2015. New England Greenhouse Floriculture Guide. A Management Guide for Insects, Diseases, Weeds and Growth Regulators. New England Floriculture Inc and the New England State Universities.

Thomas, C. 2005. Greenhouse IPM with an Emphasis on Biocontrol. Publication No. AGRS-96. 89 pp. Pennsylvania Integrated Pest Management Program.

http://extension.psu.edu/pests/ipm/agriculture/copy_of_greenhouse/greenhouse-manual

 

 

 

Disclaimer for Fact Sheets:

The information in this document is for educational purposes only.  The recommendations contained are based on the best available knowledge at the time of publication.  Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended.  UConn Extension does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.  The University of Connecticut, UConn Extension, College of Agriculture, Health and Natural Resources is an equal opportunity program provider and employer.